A week ago today the Justice Department announced the indictments of 12 members of Russian military intelligence in connection with interference in the 2016 presidential election. Their agency is called the GRU. NPR national security correspondent Greg Myre explains what it does and just what GRU stands for.

GREG MYRE, BYLINE: It's the Russian acronym for Main Intelligence Directorate of the armed forces. And here's a sampling of its work over the past decade. In 2008, a combined cyber and military attack that pummeled neighboring Georgia. More recently, critical ongoing support to bolster President Bashar al-Assad in Syria's devastating war.

MARK GALEOTTI: And then, above all, along came the Ukrainian conflict. The GRU was at the forefront of the seizure of Crimea, which is after all a textbook operation.

MYRE: That's Mark Galeotti, a British analyst who tracks the Russian intelligence services.

GALEOTTI: What's important about the GRU is basically it's a war-fighting organization. As far as the Kremlin is concerned, Russia is at war. It's a political war, but it's at war with the West.

MYRE: All this was a prelude to the 2016 hacking operation in the U.S. presidential campaign. The latest Justice Department indictment charges 12 GRU officers and breaks down the operation with names, dates, addresses and other details. Ben Nimmo works at the Atlantic Council's digital forensic lab in Washington.

BEN NIMMO: It goes down to the level of individual computers on at least one occasion. It says that the computer which was used to run account X was also used to run account Y. That's a very, very specific level of detail which they have.

MYRE: Back in Soviet times, the dominant intelligence agency was the KGB, and one of its officers then is Russia's president now, Vladimir Putin. When the Soviet Union collapsed in 1991, the KGB was broken up with separate domestic and foreign intelligence services complete with new names. The lesser-known GRU, founded a century ago by Russian revolutionary Leon Trotsky, just kept going under the same name. And about a decade ago, it seized an opportunity.

JOSEPH FITSANAKIS: The GRU saw a niche for itself. You know, what is it that they could do that other agencies in Russia were not doing at the time? And cyber was one of those.

MYRE: Joseph Fitsanakis teaches at Coastal Carolina University and specializes in spy agencies. He spoke to NPR by Skype.

FITSANAKIS: As a result, today it's sort of the cutting edge of cyber espionage operations in the Russian Federation.

MYRE: But the Russians do leave behind breadcrumbs. Here again is the Atlantic Council's Nimmo.

NIMMO: So there's an odd mix between a lot of professional hacking skill and very poor publicity surrounding it.

MYRE: He's referring to limited social media skills and poor English grammar.

NIMMO: It kept on talking about another Hillary Clinton's backer. A native English speaker wouldn't do that. It's another backer of Hillary Clinton.

MYRE: Such examples abound with Russian trolls. Consider the effort to sow discord around NFL players taking a knee before the national anthem at football games. The trolls used the hashtag #taketheknee instead of the more natural English expression take a knee.

NIMMO: So some of the linguistic clues were very, very basic but a very strong giveaway.

MYRE: No one expects those 12 indicted GRU officers to see the inside of a U.S. courtroom. And analysts say the Russian agency still appears to be on the offensive. They point to Sergei Skripal, a former GRU spy who was poisoned this spring in Britain and barely survived. According to the British press, GRU operatives are considered the main suspects. Greg Myre, NPR News, Washington.